The only objects that regularly cross the whole solar system, and the only ones you can watch do it. Eight of them drawn on their real orbits, with the next return of each solved rather than looked up.
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Distances from the sun are in AU — one AU is the Earth’s average distance, 149,597,870 km — and the angle is where the body sits around its orbit, measured from the March equinox direction.
Switch on Comets above and each of these appears on its own orbit, with a tail pointing away from the sun — which is the direction a real tail points, whatever the comet is doing. On the way out, a comet travels tail first.
| Comet | Orbit | Closest to the sun | Furthest | Next perihelion | Direction |
|---|---|---|---|---|---|
| 1P Halley | 75.32 y | 0.586 AU | 35.1 AU | Jun 4, 2061 | backwards |
| 2P Encke | 3.30 y | 0.336 AU | 4.1 AU | Feb 7, 2027 | forwards |
| 55P Tempel-Tuttle | 33.24 y | 0.977 AU | 19.7 AU | May 26, 2031 | backwards |
| 109P Swift-Tuttle | 133.28 y | 0.960 AU | 51.2 AU | Mar 26, 2126 | backwards |
| 12P Pons-Brooks | 71.33 y | 0.781 AU | 33.6 AU | Aug 22, 2095 | forwards |
| 67P Churyumov-Gerasimenko | 6.44 y | 1.243 AU | 5.7 AU | Apr 12, 2028 | forwards |
| C/1995 O1 Hale-Bopp | 2,537 y | 0.914 AU | 371.1 AU | Jan 18, 4534 | forwards |
| C/2020 F3 NEOWISE | 6,788 y | 0.295 AU | 716.7 AU | Aug 24, 8808 | backwards |
Every date in that column is computed from the comet’s orbit, not looked up — which is exactly why it should be read with care. Halley’s next perihelion comes out of this two-body model at Jun 4, 2061; the published figure, which accounts for the tug of the planets over a whole 75-year lap, is 28 July 2061. Two months of drift over three quarters of a century is what the simplification costs, and it is worth knowing the size of it.
A tail is not exhaust. It is the comet being blown apart slowly: sunlight and the solar wind strip gas and dust off the nucleus and push them directly away from the sun. So the tail swings around as the comet passes perihelion, and on the outbound leg it leads rather than follows.
There are usually two of them. The ion tail is gas, ionised by sunlight and carried straight out along the magnetic field of the solar wind — narrow, blue, and pointing exactly anti-sunward. The dust tail is heavier grains that keep some of the comet’s own orbital motion and fall behind, curving. The drawing here shows the anti-sunward direction only, because that is the part that is a geometric fact rather than a photograph.
That dust does not disappear. It stays strung out along the orbit, and when Earth crosses one of those trails we get a meteor shower on the same dates every year — the Perseids in August from 109P/Swift-Tuttle, the Leonids in November from 55P/Tempel-Tuttle. Both of those orbits are drawn on this page.
Every one of these is genuinely unsettled — not simplified for the page, not waiting on a textbook update.
It was the standard answer for decades, and then the ratios stopped matching. Rosetta measured 67P's deuterium-to-hydrogen ratio at about three times Earth's ocean value; some other comets match better. The current view is that asteroids did most of the delivering — but the sample of comets measured directly is tiny.
Nothing in it has ever been observed in place. Its existence is inferred entirely from the orbits of the comets that fall out of it. Its inner edge, its total mass and whether it is shared with other stars are all estimates.
Comets have disintegrated on approach with no impact and no obvious trigger — Schwassmann-Wachmann 3 broke into dozens of pieces, and others have vanished entirely. Rotational spin-up from outgassing is the leading explanation, but predicting which comet will survive perihelion is still not possible.
Findings reviewed August 2026. Space science moves; a date on a finding is part of the finding.
The date, the zoom, the span, the speed, the layers and any flight path are all in the address bar, so copying the URL shares exactly what is on screen. Set it up above, then take the link — it is the quickest way to hand a class one specific thing to look at.
This one is about the whole system. If the question is where the sun and the moon are from where you are standing — what time the sun comes up, why tonight's moon is the shape it is — that is the Sun, Earth & Moon movement simulator, which has a page for every city and a slider over a day, a week or a month.
The asteroid belt · Also: the classroom guide · sunrise & sunset by city · moon phase & moonrise · lunar eclipses · how the positions are worked out
Did comets bring Earth's water? It was the standard answer for decades, and then the ratios stopped matching. Rosetta measured 67P's deuterium-to-hydrogen ratio at about three times Earth's ocean value; some other comets match better. The current view is that asteroids did most of the delivering — but the sample of comets measured directly is tiny.
What is the Oort cloud actually like? Nothing in it has ever been observed in place. Its existence is inferred entirely from the orbits of the comets that fall out of it. Its inner edge, its total mass and whether it is shared with other stars are all estimates.
Why do some comets simply fall apart? Comets have disintegrated on approach with no impact and no obvious trigger — Schwassmann-Wachmann 3 broke into dozens of pieces, and others have vanished entirely. Rotational spin-up from outgassing is the leading explanation, but predicting which comet will survive perihelion is still not possible.